Apparatus and method for removing mercury and mercuric compounds from dental effluents

ABSTRACT

The present invention is directed to processes for removing a contaminant from dental effluents and includes transporting a three-phase effluent through a suction line into a particle collection vessel, introducing a suction line cleaning solution which includes a reagent into the suction line, and introducing the three phase effluent and the line cleaning solution into the collection vessel, wherein the effluent separates into solid. liquid, and gas phases in the collection vessel and the reagent includes a flocculant and/or a precipitant. and removing the gaseous and liquid phases from the collection vessel. The contaminant includes mercury. lead. and arsenic.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 09/794,577 filed Feb. 27, 2001, entitled “APPARATUS AND METHODFOR REMOVING MERCURY AND MERCURIC COMPOUNDS FROM DENTAL EFFLUENTS” (nowU.S. Pat. No. 6,797,178), which claims the benefits of U.S. ProvisionalApplication Ser. Nos. 60/191,916, filed Mar. 24, 2000; 60/239,463, filedOct. 10, 2000; and 60/267,6 14, filed Feb. 9, 2001, all of which areincorporated herein by reference in their entireties.

NOTIFICATION OF FEDERAL RIGHTS

This invention was made with Government support under Grant No.5R44DE13081-03 awarded by the National Institutes of Health. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates generally to removing mercury andmercury-containing compounds from liquid wastes and specifically toremoving mercury and mercury-containing compounds from dental effluents.

BACKGROUND OF THE INVENTION

Each year tens of thousands of pounds of mercury-containing wastes aredischarged by dental offices into municipal waste systems. Amalgamfillings typically contain about 50% mercury by weight. Mercury is aknown environmental contaminant, classified by the USEPA as apersistent, bioaccumulative, and toxic material. Waste water treatmentplants must meet strict limits on the amount of mercury they canrelease. The discharged form of mercury is typically highly toxic (i.e.,unstable) and in violation of applicable environmental regulations.Although particulate removal systems used in some dental offices removemercury-containing particles, they do not remove dissolved mercury andmercury-containing compounds. Examples of such devices are described inU.S. Pat. Nos. 5,885,076; 5,797,742; 5,795,159; 5,577,910; 5,227,053;4,753,632; 4,591,437; 4,385,891; and 5,114,578, all of which areincorporated herein by this reference.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for removing solidamalgam particles and/or soluble forms of mercury and other metals (suchas silver) and other contaminants from dental effluents.

In one embodiment, a contaminant removal system is provided for treatinga three-phase effluent. The system includes:

-   -   (a) a particle collection vessel for separating a gas phase, a        liquid phase, and a solid (particulate) phase in the three-phase        of effluent;    -   (b) a first discharge line from the vessel for removing the        liquid phase from the vessel;    -   (c) a second discharge line from the vessel for removing the gas        phase from the vessel; and optionally    -   (d) a liquid treatment device for removing and/or stabilizing        contaminants in the liquid phase to form a treated liquid phase.        The contaminant can be any undesirable organic or inorganic        material in the effluent. Examples include metals (e.g.,        mercury, lead, arsenic, etc.), metal compounds, bacteria,        pathogens, inorganic and organic solvents, and mixtures thereof.

The particle collection vessel can be of any suitable design. Forexample, the vessel can be a settling tank, a sedimentation device, acentrifuge, or any other device that utilizes gravity or centrifugalforces for effectuating solids/liquid separation. In one configuration,the particle collection vessel includes one or more baffles tofacilitate solid/liquid/gas separation.

To remove the liquid phase from the particle collection vessel, thesystem can include a timer connected to a pump on the first dischargeline to cause periodic removal of the liquid phase from the vesselduring periods when no waste is incoming (e.g., overnight). In thismanner, the liquid is provided with a relatively quiescent period foreffective settlement of entrained particles such as amalgam particles.

The liquid treatment device can be any suitable device for removingand/or stabilizing contaminants in the liquid phase to form the treatedliquid phase. In one configuration, the liquid treatment device includesone or more devices for adding chemical additives, such as one or moreof a pH adjustor, an oxidant, a reductant, and a precipitant with theliquid phase. In one configuration, the liquid treatment device includesone or more sorbent columns that contact the liquid phase with one ormore sorbents.

The effluent can be any contaminated effluent regardless of the source.In a preferred configuration, the effluent is produced by dental work ona patient. The effluent is collected by a liquid collection device, suchas a sink, suction tube or, evacuation line, and conveyed to theparticle collection vessel via a waste discharge line. A single particlecollection vessel can service a plurality of such liquid collectiondevices corresponding to a plurality of dental chairs.

In another embodiment, a process is provided for removing dissolvedcontaminants from the three-phase effluent. The process includes thesteps of:

-   -   (a) introducing the three-phase effluent into a particle        collection vessel;    -   (b) reducing the velocity of and/or redirecting the direction of        movement of the effluent, thereby causing a solid phase and a        liquid phase to separate from a gas phase;    -   (c) removing the gas phase from the collection vessel;    -   (d) removing the liquid phase from the collection vessel; and        optionally    -   (e) contacting the liquid phase with at least one of an additive        and a sorbent to form a treated liquid phase.

As noted, the liquid phase can be removed discontinuously from thecollection vessel to provide more effective separation of the entrainedparticles from the liquid phase.

In one configuration, the contacting step further includes the steps of;

-   -   (f) first contacting the liquid phase with one or more of a        reductant, an oxidant, a participant, and a pH adjustor I        (typically prior to removal of the liquid phase); and    -   (g) second contacting the liquid phase with a sorbent to remove        mercury therefrom. In another configuration, step (g) is        optional.

As will be appreciated, the additive, preferably a reactant (a compoundthat will react with the contaminant, such as a reductant, oxidant,and/or precipitant), maybe used in the absence of (or without) asorbent. For example, the reactant could be a precipitant that forms aprecipitate with the contaminant. The precipitate could be removed fromthe effluent by ifitration techniques, gravity separation techniques,etc. A flocculant, such as aluminum or commercially available polymers,could be further added to the effluent to act as a filter and/orsettling aid.

The system and method can provide numerous benefits. For example, thesystem can remove not only solid amalgam particles but also removeand/or stabilize dissolved elemental mercury and speciated mercury. Thesystem and method can be effective at capturing a high percentage of theamalgam particles. The vessel typically captures or collects at leastmost and more typically at least about 95% of all amalgam particles thatare about 10 microns or greater in size. The chemical treatment devicecan further remove at least most of the amalgam particles that are lessthan about 10 microns in size. Amalgam particles typically represent atleast 95% of the total mercury sent to the system. Any of the systemcomponents can be used as a recycling device. For example, thecollection vessel or sorbent column can be operated for a predeterminedperiod (typically 6–12 months) after which the vessel and/or column isreplaced. The used vessel and/or column is shipped to a recyclingfacility to recover the captured amalgam particles and/or elemental andspeciated mercury. The system can operate effectively without a sorbent.Proper selection of the additives can remove the need for a sorbent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a particulate collection vessel inaccordance with one embodiment of the present invention;

FIG. 1B is a flow schematic of the embodiment of FIG. 1A;

FIG. 2 is a side view of the vessel;

FIG. 3 is a side view of the baffle assembly;

FIG. 4 is a side view of the cap to the vessel;

FIG. 5A is a plan view of the cap;

FIG. 5B is a cross-sectional view of the particulate collection vesselin operation;

FIG. 6 is a top view of the cap according to another embodiment of thepresent invention;

FIG. 7 is a perspective view of the particulate collection system;

FIG. 8 is a side view of the baffle assembly engaging the spacingassembly;

FIG. 9 is a top view of the spacing assembly;

FIG. 10 is a side view of the cap;

FIG. 11 is a block diagram showing the various components of a mercuryremoval system according to another embodiment of the present invention;

FIG. 12 is a view of the various components installed in an enclosure;

FIG. 13 is a cross-sectional view taken along line 10-10 of the sorbentcolumn of FIG. 9;

FIG. 14 is a graph of final mercury concentration (PPB) (vertical axis)against reagent (horizontal axis); and

FIG. 15 is a plot of mercury concentration (ppb) (vertical axis) versussample number (horizontal axis).

DETAILED DESCRIPTION

The Particulate Collection System

A first embodiment of the present invention is depicted in FIGS. 1–5 and7. The particulate collection system 100 includes a collection vessel104, a pump 108 (e.g., a peristaltic pump), and a timer 112 (e.g., anelectronic 24/7 timer). The collection vessel 104 is located between thevacuum line 116 to the chairs 118 a–n and the vacuum line 120 to thevacuum pump 124. Thus, the vessel 104 is typically installed on thesuction side of the vacuum pump 124, preferably close to the vacuumpump. A liquid discharge line 128 is connected to the pump 108 and fromthe pump 108 to the exhaust hose 132 from the vacuum pump 124 to thesewer (not shown).

The timer 112 is connected to the pump 108 to cause discontinuousdischarge of the liquid waste (or liquid phase) from the collectionvessel 104. The timer 108 ensures that there is a sufficient(predetermined) settling time (in which the liquids and solid phases arerelatively quiescent) prior to activating the pump 108 to discharge the(supernatant) wastewater or liquid phase. Typically, the predeterminedsettling time (between pump activation cycles) ranges from about 1 toabout 24 hrs and more typically from about 8 to about 12 hrs. Thedischarge is performed at a controlled, slow rate (typically in therange of from about 10 to about 1000 ml/min and more typically in therange of from about 20 to about 200 ml/min).

FIGS. 2–5 depict the various components of the collection vessel 104.The collection vessel 104 includes a central housing 150, a base 154attached to the bottom of the housing 150, a cap 158 attached to the topof the housing 150, a dip tube 162 connected to passage 166 in the cap158, and a baffle assembly 170. The dimensions of the vessel 104typically range from about 10 to about 25 inches high and about 5 toabout 25 inches in diameter.

The baffle assembly 170 includes a cylindrical baffle tube 174 having aplurality of supporting legs 178 a–c spaced at intervals around thebottom of the baffle tube 174. The inner and outer radii of the baffletube 174 are less than the inner radius of the housing 150 so that thebaffle assembly can be received inside of the housing. Typically, theinner and outer radii of the baffle tube 174 are no more than about 50%of the inner housing 150 radius and typically are no less than about 10%of the inner housing 150 radius. The baffle tube 174, of course, has ahollow interior to permit fluids to flow upwardly and/or downwardlythrough the tube as shown. The dip tube 162 is positioned inside of thebaffle tube 174 during use and at or near the central vertical axes ofthe housing 150. The baffle tube 174 is located such that the dip tube162 and the cap outlet port 180 a are located inside the cylindricalhousing of the tube.

The cap 158 includes two conduits 180 a,b that pass through the cap 158and project a distance “D₁” (typically from about 0.5 to about 3 inchesbelow the cap surface 184. The conduits 180 a,b connect to the vacuumlines 120 and 116, respectively. The distance “D” is sufficient to holdthe baffle tube 174 in position within the housing 150 (i.e., underports 166 and 180 a) during use.

The collection vessel 104 and baffle assembly 170 can be made of anysuitable material, with corrosion resistant plastics, such as PVC beingpreferred.

In operation, a three-phase mixture 117 of gas, solids or particles(e.g., mercury amalgam particles), and liquid from the dental chair(s)passes through vacuum line 116 and into the annular area 190 between theexterior surface 192 of the baffle tube 170 and the interior surface 188of the housing 150. The velocity of the mixture is slowed by the largeflow area within the vessel, causing solid particles 189 to settle outof the mixture and collect in the bottom of the housing 150. The gasphase 118 of the mixture passes above (i.e., the top 190 of the baffletube 170 is typically spaced from the cap bottom 184) and around baffletube 170 (i.e., the baffle tube exterior 192 is typically spaced fromthe housing interior around the baffle tube's periphery). The liquidphase 119 also settles out of the gas phase (due to the decrease in gasvelocity) and collects in the bottom of the housing with the particles.Baffle tube 170 forces the liquid flow between legs 178 a–c in order toexit vessel 150 via either dip tube 162 or outlet port 180 a. This flowpath will create some particle separation (albeit less than in normaloperation) in the event that the vessel 150 overflows. Periodically, thepump 108 is activated by the timer 112 and draws collected liquid phaseout of the bottom of the housing via dip tube 162 and discharges theliquid phase through discharge line 128 into the exhaust hose 132. Thepump 108 is typically activated at a time interval ranging from about 5mins. to about 12 hrs, more typically from about 2 to about 12 hours,and even more typically from about 2 to about 6 hours. The flow rate ofpump 108 is low enough, typically about 0.02 to about 1 l/min., toprevent entrainment of the settled particles. The dip tube 162 designprevents particles from being withdrawn with the liquid and, therefore,the particles remain in the bottom of the housing 150.

The system has numerous operational benefits. The system can beeffective at capturing about 95% of all particles that are greater thanabout 10 micron in size. This fraction of particles typically amounts toabout 95% of the total mercury sent to the system. The system can be aself-priming system and will hold a vacuum when turned off. The pump canrun dry without damaging the motor or the drive unit. The unit can beused as a recycling device. After the unit operates for a predeterminedperiod (typically six to twelve months) the vessel is replaced with anew vessel and the used vessel shipped to a recycling facility torecover the captured amalgam particles. The vessel can remove fineamalgam particles that can damage the dental vacuum pump.

Installation of the system depends on the application. The system isdesigned to work with either wet- or dry-vacuum systems. In a dry-vacsystem, it is preferred that the vessel be installed upstream of the dryvac's air/water separator. The existing air/water separator may beremoved; however, it is recommended that the existing air/waterseparator be left in place to protect the vacuum pump in the event thatthe vessel overfills. Because liquids will not damage a wet-vac pump, nosuch precaution is required for a wet system. If installed downstream ofan existing air/water separator, the system is typically installed toreceive the liquid outlet flow from the air/water separator. Differentsize clinics can be accommodated by adjusting the overall size of thesystem. In one configuration, the system is designed so that if anyproblem occurs with the unit, fluid flow will bypass the vessel andallow continued operation of the dental suction system.

FIGS. 6 and 8–10 show a particle collection system according to anotherembodiment of the present invention. The baffle assembly 200 includes aspacer assembly 204 that engages the upper end of the baffle tube 170.Spacers 208 a–c are positioned at intervals around the periphery of thebaffle tube 170 to maintain the correct, spaced relationship between thetube wall and the housing interior. Because the spacer assembly 204maintains the tube exterior in a spaced apart relationship relative tothe housing wall, the cap 210 does not require downwardly projectingconduits 180 a,b.

The Combined Particulate Removal and Purification System

Referring to FIGS. 11–13, the combined particulate removal andpurification system 300 will now be discussed. The system removes and/orstabilizes soluble forms of mercury as well as solid-phase mercury.Soluble forms of mercury are typically present in the dental wastewaterfrom the reaction of the mercury in amalgam particles with thewastewater which releases soluble forms of mercury into the wastewater.

The system 300 includes the particulate collection vessel 104 describedabove and, in addition, a chemical doser 304 and a sorbent column 308and sub-micron filter 309. The doser 304 and sorbent column 308 are incommunication with discharge line 312 and pump 108. Pump output line 312b is connected to the doser 304 and an output line 312 c from the doser304 is connected to the sorbent column 308. The output line 312 d fromthe sorbent discharges into the sewer or line 128.

As will be appreciated, the dissolved mercury-containing compounds,colloidal mercury, and small (e.g., less than about 10 microns) amalgamparticles in the waste liquid from the particulate collection vessel areremoved and/or stabilized by the doser 304 and sorbent column 308 andpolishing sub-micron filter 309.

One or more dosers 304 can be used to directly reduce mercury levels inthe wastewater and/or adjust wastewater chemistry. A doser willtypically release one or more suitable additives to the wastewater tomaintain desirable chemical properties, to convert dissolved mercury toa less soluble form of mercury, or enhance the performance of amercury-selective sorbent in the sorbent column 308 in removingdissolved mercury from dental amalgam wastewater, and/or to kill orneutralize organic material in the wastewater. Suitable solid additivesare preferably nontoxic and sparingly soluble in the wastewater so thatthey are slowly released into the water. Alternately, the additive couldbe added by any other suitable technique. For example, the additive canbe slowly added (as a liquid, solid, or gas) via a dosing mechanism(e.g., a pump) or by encapsulation in a slowly dissolving substance.

In another embodiment, the reagent can be added to the collection vesselvia the dental suction line. For example, most dental offices flush asuction line cleaning solution through their evacuation system. Thereagent could be added in the same method, or be co-blended, with theline cleanser. In this case, the additive is added to and in theeffluent upstream of the collection vessel and further additiveaddition(s) in or downstream of the collection vessel is/are optional.The blending could be done during or after production of the cleanser.The blending can be done by known techniques such as by using a ribbonblender. Typical dental line cleansers contain surfactants anddisinfectants and may range in pH from acid to highly basic. Activeingredients include sodium hydroxide (Alprojet™), chloramine T (Tiutol™,Aseptoclean 2™), sodium perborate or another percarbonate, hydrogenperoxide (Orotol Ultra™), ammonium chloride (S&M matic™, Vacusol™),sodium hypochlorite (bleach), pyridine compounds (Green & Clean™),phosphoric acid (Purevac™), glycolic acid, citric acid, isopropanol,chlorhexidine gluconate (Biovac™), and/or enzymes (Vacukleen™). In thiscase, any of these cleansers would further include one or more of theadditives of the present invention.

The doser 304 can be of any suitable design. The doser may include aseparator contacting chamber or may add reagent directly into collectionvessel 104. In one design, the doser 304 includes inner and outercontainment vessels 320 a,b forming annulus 322 therebetween and a bed336 of additive particles contained within the inner containment vessel320 b. Wastewater 328 flows in the annulus 322 between the inner andouter containment vessels, through the space 332 between the bottoms336, 340 of the inner and outer containment vessels 320 b,a, and throughthe (fluidized) bed 336 in the inner containment vessel 320 b. Inanother design, the dosing occurs within the amalgam separator 104itself.

In one configuration, the doser contacts an additive (or pH adjustor)for controlling wastewater pH. The additive can be any suitablesubstance for controlling pH, such as a base, e.g. hydroxides,carbonates, and phosphates with hydroxides and carbonates beingpreferred, or acid, e.g., organic acid and mineral acids, with mineralacids being preferred. Sufficient pH adjustor added to maintain a pHpreferably ranging from about pH2 to about pH6 or from about pH8 toabout pH10, depending on the application. pH adjustment is used toenhance the performance of other additives or of sorbent materials.Sorbents often work better at low pH, whereas many precipitatingadditives require a high pH.

In one configuration, the doser 304 contacts an oxidant with thewastewater to oxidize organic matter before passing the wastewaterthrough the sorbent column. As will be appreciated, organic matter canclog, bio-foul, or otherwise impair the performance of the sorbentmaterial. Any suitable oxidant can be used. Preferred oxidants includeorganic halogen derivatives (e.g., symclosene, oxyhalide salts (e.g.,hypochlorite), ozone, hydrogen peroxide and/or organic peroxides). Intypical applications, the amount of oxidant added will range from about10 to about 1000 ppm.

In another configuration, a reductant is contacted by the doser with thewastewater to reduce mercury-containing compounds and materials.Reducing agents minimize oxidation and release of mercury from capturedamalgam and helps to chemically reduce incoming oxidized mercury,thereby making it less soluble. For example, reduced elemental mercuryhas a very low solubility—on the order of 20 micrograms/L. Any suitablereductant can be used. Preferred reductants include stannous chloride,iron, tin oxalate, bisulfites, and/or polyvalent metals.

A reducing additive should create a solution oxidation/reductionpotential capable of reducing oxidized forms of mercury back toelemental mercury. The standard electrode potentials (E°) for mercurous(Hg₂ ⁺⁺+2c=2ē) and mercuric (Hg⁺⁺+2ē=Hg) reduction are about +0.789 Vand +0.854 V respectively. These are measured versus a standard hydrogenelectrode. Thus to create a solution environment where the concentrationof oxidized mercury is no greater than that for elemental mercury (theassumed minimum limit for a solution in contact with amalgam) therequired potential is given by:

$\begin{matrix}{{Eh} = {{E{^\circ}} + {0.059\mspace{11mu}{\log\left( \frac{\left\lbrack {Hg}_{oxidized} \right\rbrack}{a_{Hg}} \right)}}}} & {{Eq}.\mspace{14mu}(1)}\end{matrix}$at 25° C. In Equation (1), the activity of elemental mercury, a_(Hg), isequal to unity by convention, and [Hg_(oxidized)] represents the molarconcentration of oxidized mercury. The equation is exact if speciesactivity is used in place of concentration. Assuming a desired minimumconcentration of 10⁻⁷ molar (˜20 ppb), the solution Eh is preferablyabout ≦+0.38 V. In typical applications, the amount of reductant addedwill range from about 10 to about 1000 ppm.

In another configuration, a precipitant is contacted by the doser withthe wastewater to cause precipitation of mercury-containing compounds asinsoluble mercury precipitates. Any suitable precipitant can be used.Preferred precipitants include iodates, sulfides and polysulfides,thioamides (e.g., thioacetamide), carbamates and thiocarbamates (e.g.,sodium diethylthiocarbamate), polycarbamates, thiocarbamides, andpolymeric or immobilized variants of these functional groups andmixtures and derivatives thereof. Carbamates are preferred as they aregenerally nontoxic and pH insensitive. In general, the precipitant canbe any chemical which forms a sparingly soluble or readily filterablecomplex with mercury or mercury-bearing compounds. In typicalapplications, the amount of precipitant added will range from about 10to about 1000 ppm.

In some configurations, the processes and compositions of U.S. Pat. Nos.5,880,060; 5,667,695; 5,370,827; 5,330,658; 5,080,799; 4,108,769; and/or4,072,605, all of which are incorporated herein by this reference, areused as or in lieu of the doser.

When a precipitant is used, a particle filter, such as a fine screen ormembrane, can be located in or downstream of the doser and in orupstream of the sorbent column (if a sorbent column is present) toremove precipitated mercury particles. The filter preferably has a poresize sufficient to remove the particles, which typically ranges fromabout 10 to about 0.45 microns. In one configuration, the particlefilter is located downstream of the sorbent column (FIG. 11).

The sorbent column 308 can be of any suitable design. The sorbent columncan be configured to contain one or multiple sorbent beds of the same ordiffering sorbents. The typical column design is a packed-bed of sorbentparticles. Other column designs include monolithic sorbent structuresand fluidized bed designs.

Referring to FIG. 13, the sorbent column 308 of one design includes acolumn housing 350, a bottom 354 having an input port 358, a top 362having an output port 366, a plurality of retaining rings 370 a–c, and aplurality of screens 374 a-c. The screens prevent intermixing of thesorbent beds 380 and 384 and restrain movement of the sorbent particlesin the beds so as to prevent clogging of the input port 358 or outputport 366 or removal of the sorbent particles from the column with thewastewater.

The sorbent can be any sorbent capable of collecting mercury. Preferredsorbents include one or more of activated carbon, ion exchange resinssuch as cellulosic resins (e.g., as discussed in U.S. Pat. No. 5,907,037which is incorporated herein by this reference) chelating resins andporous silica, and zeolites.

In a preferred configuration, the first sorbent bed 380 of activatedcarbon is located near the input port 358 to remove dissolved mercuryand residual oxidant (if added previously by a chemical doser 304) fromliquid 119 and the second sorbent bed 384 of an ion exchange resin islocated above the first sorbent bed near the output port 366 to removefurther dissolved mercury from liquid 119.

The purified wastewater 390 is fully compliant with pertinentenvironmental regulations. Typically, the purified wastewater 390contains no more than about 10 ppb mercury.

In operation, the wastewater 328 is removed from the vessel 104 asdescribed above and passed through the input at the top of the doser304, through the annulus 322 and through the additive bed 336, and isremoved through the output at the top of the doser 304 to form a treatedwastewater. The treated wastewater 400 is introduced into the sorbentcolumn 308 through input 358, passed sequentially first through sorbentbed 380 and second through sorbent bed 384 to form a purified wastewater390. The wastewater is filtered with a polishing filter 308 to removesorbent residue. Purified wastewater 390 can be discharged directly intothe sewer.

EXPERIMENTAL ISO Certification

The international organization for standardization (ISO) is a worldwidefederation of national standards bodies. ISO standards provide safetyand performance guidelines for a variety of equipment categories,including dental equipment. International standard ISO 11143 wasprepared by the ISO dentistry technical committee to assess theperformance of dental amalgam separators.

Amalgam separators are defined as items of dental equipment designed toretain amalgam particles carried by the wastewater from the dentaltreatment system, so as to reduce the number of amalgam particles andtherefore the mercury entering the sewage system. The use of acentrifuge, filtration, sedimentation or combination of any of thesemethods may achieve separation of the amalgam particles.

ISO 11143 specifies requirements for amalgam separators used inconnection with dental equipment in the dental treatment system. Itspecifies the efficiency of the amalgam separator (minimum of 95%) interms of the level of retention of the amalgam based on a laboratorytest. The standard also describes the test procedure for determiningthis efficiency, as well as requirements for the safe functioning of theseparator, labeling, and instructions for use of the device. The groundamalgam sample for the efficiency test of the amalgam separator isdivided into three different fractions:

-   -   6.0 g of particles sized 3.15 mm to 0.5 mm    -   1.0 g of particles sized 0.5 mm to 0.1 mm    -   3.0 g of particles smaller than 0.1 mm

In addition, 50% of the fine fraction particles should be less than 0.01mm. The test sample used to assess the efficiency of the amalgamseparator has a particle size distribution that reflects the situationfound in dental treatment systems. The size fractions used in thestandard are based on investigations that have been carried out todetermine the particle size distribution of amalgam particles in waterfrom dental treatment systems.

In summer 2000, the BullfroHg™ amalgam separator was independentlytested following ISO 11143. The separator received a score of 99.6%removal efficiency when empty and 98.6% efficiency when full, easilypassing the required test efficiency of 95%.

ISO CERTIFICATION TEST RESULTS Reference/Equipment: Amalgam SeparatorBullfroHg ™ Rating: Rated voltage: 120 V AC Rated current: 1.5 amp Dateof receipt: Jun. 22, 2000 Type of examination: Alternate constructiontest. Test regulations: 1SO 11142: 1999-12 Testing period: July/August2000 Test location: Technology Centre of RWTUV Analagentechnik GmbHClassification: Type 2: Sedimentations system Amalgam sample: BeckerMeBtechnik GmbH, 71364 Winnenden, Germany ISO 1O g, January 2000 Maximumwater floulrate: 750 ml/mn., 10 l altogether Type of membrane filters:Schleicher + Schuell Membrane filters AE 100 + ME29 + ME28 Number oftests performed: 6 Separation degrees of empty amalgam separator: after12 to 14 hours 1. 99.9% 2. 99.7% 3. 99.3% Average 99.6% Separationdegrees of full amalgam separators: after 12 to 14 hours 1. 99.0% 2.98.0% 3. 97.9% Average: 98.3% Value of the efficiency: 98.3% Annex (No.Of pages): None Test result: The referenced units are in compliance withthe above requirements. Test program ISO 11143 Denta Equipment-AmalgamSeparators: 1999 Test object: Amalgam Separator Model BullfroHg ™Classification: Type 2: Sedimentation system Amalgam sample: BeckerMeBtechnik GmbH 71364 Winnenden, Germany ISO 10 g, January 2000 Maximumwater flow/rate: 750 ml/min., 10 1 altogether Type of membrane filters:Schleicher + Schuell Membrane Filters AE 100 + ME29 + ME28 Number oftests performed: 6 Separation degrees of empty amalgam separator: after12 to 14 hours 1. 99.9% 2. 99.75 3. 99.3% Average: 99.6% Separationdegrees of full amalgam separators after 12 to 14 hours 1. 99.0%2. 98.0% 3. 97.9% Average.

Value of the efficiency: 98.3%

The BullfroHg™ Hg amalgam separator passed the test.

In addition to the ISO test, ADA further performed an initial screeningof the doser concept. The tests were intended to demonstrate thatmercury levels could be reduced by reagent addition. Dental waste from aDenver-area clinic was used in these tests. The wastewater was firstifitered through a 10-micron filter to remove large particles. Some ofthe wastewater was sent through a 0.45-micron filter to determine theamount of “soluble” mercury. The tests consisted of 150 mL of waste and10 g of reagent placed into 250-mL shaker flasks. The flasks were shakenovernight and the solutions in each flask were again ifitered with a10-micron filter to remove solids. Half of the samples were thenfiltered through a 0.45-micron filter. The results are plotted in FIG.14.

Sixteen different reagent combinations were tested in these firsttrials. Several reduced the amount of mercury in the wastewater sample.Of those tested, iron, calcium carbonate, potassium iodate and tinoxalate appear to yield the best results. Some tested reagentssuccessfully reduced the mercury levels, but are not believed to bepractical for other reasons.

These initial tests were intended to demonstrate that mercury levelscould be reduced by addition of a reagent. Reagents other than thosetested are also possible.

In addition to the above tests, the City of Toronto carried outindependent testing of a system as depicted in FIGS. 11 and 12. Thesystem was connected to a city dental clinic suction system and theeffluent 390 was analyzed for total mercury concentration. The resultsare depicted in FIG. 15. The system consistently reduced the mercuryconcentration to less than 10 micrograms per liter—levels that cold notbe achieved through particle separation alone.

The foregoing description of the present invention has been presentedfor purposes of illustration and description. Furthermore, thedescription is not intended to limit the invention to the form disclosedherein. Consequently, variations and modifications commensurate with theabove teachings, in the skill or knowledge of the relevant art, arewithin the scope of the present invention. For example, the particulatecollection vessel can be used without the addition of an additive or theuse of a sorbent. The embodiments described here and above are furtherintended to explain best modes for practicing the invention and toenable others skilled in the art to utilize the invention in such, orother, embodiments and with various modifications required by theparticular applications or uses of the present invention. It is intendedthat the appended claims be construed to include alternative embodimentsto the extent permitted by the prior art.

1. A process for removing a contaminant from a three-phase dentaleffluent, comprising: transporting a three-phase effluent from dentalwork on a patient through a suction line into a collection vessel,wherein the effluent comprises one or more contaminants; contacting aliquid phase of the three-phase effluent with at least one reagent;introducing the three-phase effluent into the collection vessel, whereinthe three-phase effluent separates into a solid phase, the liquid phase,and a gas phase in the collection vessel and the at least one reagentcomprises at least one of an agglomerating agent and a precipitatingagent to improve the collection efficiency for one or more contaminants;removing the gas phase from the collection vessel; and removing theliquid phase from the collection vessel, wherein the at least onereagent is contained in a line cleaning solution and wherein the linecleaning solution is introduced into the suction line in the contactingstep.
 2. The process of claim 1, wherein the at least one reagentcomprises the precipitating agent and reacts with mercury-containingcompounds in the three-phase effluent to form a mercury-containingprecipitate.
 3. The process of claim 2, wherein the reagent is one ormore of an iodate, a polysulfide, a sulfide other than a polysulfide, athioamide, a carbamate other than a thiocarbamate, a thiocarbamate, athiocarbamide, and polymeric or immobilized variants of the foregoing.4. The process of claim 1, wherein the at least one reagent comprises areducing agent to reduce oxidized mercury-containing compounds.
 5. Theprocess of claim 4, wherein the at least one reagent comprises apolyvalent metal.
 6. The process of claim 4, wherein the at least onereagent is one or more of stannous chloride, iron, tin oxalate, and abisulfite.
 7. The process of claim 4, further comprising: maintaining anoxidation-reduction potential, Eh, of the liquid phase of no more thanabout 0.38 Volts.
 8. The process of claim 1, wherein the suction linecleaning solution comprises one or more of sodium hydroxide, chloramineT, a percarbonate, sodium perborate, hydrogen peroxide, ammoniumchloride, sodium hypochlorite, pyridine compounds, phosphoric acid,glycolic acid, citric acid, isopropanol, chlorhexidine gluconate, andenzymes.
 9. The process of claim 1, wherein the suction line cleaningsolution comprises a pH adjustor and further comprising: maintaining apH of the liquid phase in the range of from about pH 8 to about pH 10.10. The process of claim 9, wherein the pH adjustor comprises at leastone of a hydroxide, a carbonate, and a phosphate.
 11. The process ofclaim 1, wherein the at least one reagent comprises an agglomeratingagent.
 12. The process of claim 11, wherein the agglomerating agent is aflocculant.
 13. The process of claim 12, wherein flocculant is apolymeric flocculant.
 14. The process of claim 1, wherein thecontaminant is a metal.
 15. The process of claim 14, wherein thecontaminant is one or more of mercury, lead, and arsenic.
 16. A processfor removing a contaminant from a three-phase dental effluent,comprising: transporting a three-phase effluent from dental work on apatient through a suction line into a collection vessel, wherein theeffluent comprises one or more contaminants; contacting a liquid phaseof the three-phase effluent with at least one reagent, wherein the atleast one reagent comprises a reducing agent to reduce oxidized forms ofmercury to elemental mercury; after the contacting step, maintaining anoxidation-reduction potential Eh of a liquid phase of the effluent to nomore than about 0.38 Volts; introducing the three-phase effluent intothe collection vessel, wherein the three-phase effluent separates into asolid phase, the liquid phase, and a gas phase in the collection vessel;removing the gas phase from the collection vessel; and removing theliquid phase from the collection vessel, wherein the at least onereagent is contained in a line cleaning solution and wherein the linecleaning solution is introduced into the suction line in the contactingstep.
 17. The method of claim 16, wherein the at least one reagentcomprises at least one of an agglomerating agent and a precipitatingagent.
 18. The process of claim 17, wherein the at least one reagentcomprises the precipitating agent and reacts with mercury-containingcompounds in the three-phase effluent to form a mercury-containingprecipitate.
 19. The process of claim 18, wherein the reagent is one ormore of an iodate, a polysulfide, a sulfide other than a polysulfide, athioamide, a carbamate other than a thiocarbamate, a thiocarbamate, athiocarbamide, and polymeric or immobilized variants of the foregoing.20. The process of claim 17, wherein the at least one reagent comprisesan agglomerating agent.
 21. The process of claim 20, wherein theagglomerating agent is a flocculant.
 22. The process of claim 21,wherein flocculant is a polymeric flocculant.
 23. The process of claim16, wherein the reducing agent comprises a polyvalent metal.
 24. Theprocess of claim 16, wherein the reducing agent is one or more ofstannous chloride, iron, tin oxalate, and a bisulfite.
 25. The processof claim 16, wherein the suction line cleaning solution comprises one ormore of sodium hydroxide, chloramine T, a percarbonate, sodiumperborate, hydrogen peroxide, ammonium chloride, sodium hypochlorite,pyridine compounds, phosphoric acid, glycolic acid, citric acid,isopropanol, chlorhexidine gluconate, and enzymes.
 26. The process ofclaim 16, wherein the suction line cleaning solution comprises a pHadjustor and further comprising: maintaining a pH of the liquid phase inthe range of from about pH 8 to about pH
 10. 27. The process of claim26, wherein the pH adjustor comprises at least one of a hydroxide, acarbonate, and a phosphate.
 28. The process of claim 16, wherein thecontaminant is a metal.
 29. The process of claim 28, wherein thecontaminant is one or more of mercury, lead, and arsenic.